As shown in FIG. 2, the polymer electrolyte fuel cell (fuel cell) 20 is constructed by stacking a plurality of unit cells 10 with electrodes called separators (or bipolar plates) 1 in between, with a solid polymer electrolyte film (solid polymer film) 12 embraced by an anode electrode (anode part) and a cathode electrode (cathode part) as a unit cell 10.
For the material of the separator for a fuel cell, the characteristic that the contact resistance is low which is to be maintained for a long period of time during use as a separator is required. As the materials with such characteristics, conventionally, application of metallic materials such as an aluminum alloy, stainless steel, nickel alloy, titanium alloy have been studied in consideration of the aspects of workability and strength as well.
On the other hand, for a separator for a fuel cell for an automobile (hereinafter referred to as a “separator”), for example, downsizing, weight reduction, and cost reduction have been strongly required. In this regard, aluminum is expected as one of the promising materials because it is light in weight, with excellent workability, and of low cost compared with stainless steel and titanium alloy.
Further, because the environment inside the fuel cell where the separator is placed is of high temperature and acid atmosphere, when the separator is constructed of a pure aluminum substrate, the surface of the aluminum substrate is corroded in a short period of time, the aluminum ions are eluted from the substrate, the electric resistance increases by a corrosion product generated on the surface of the substrate, and the function as a separator is not exerted.
With reference to such problems, Patent Document 1 describes a separator wherein any of a carbon layer, silicon carbide layer, nickel layer, chromium layer, tin layer is formed on the surface of the aluminum substrate with the aim of allowing the aluminum substrate to have both the corrosion resistance and the electrical conductivity. Also, Patent Document 2 and Patent Document 3 describe a separator wherein a porous anodic oxide film is formed first on the aluminum substrate attaching importance to the corrosion resistance, and an electrically conductive film (dielectric breakdown region) is formed on its surface or in a hole. Patent Document 4 describes a separator including an aluminum substrate and a resin layer containing an electrically conductive material formed to cover the aluminum substrate through a first intermediate layer having a nickel plating layer or a copper plating layer and a second intermediate layer having a tin plating layer or a tin alloy plating layer.
Prior Art Literature
Patent Document
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2000-58080
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2006-49209
[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2005-243595
[Patent Document 4] Japanese Unexamined Patent Application Publication No. 2009-32671